When Modifying Curves Don LaCourse, eDocHelp
November 16, 2004
reprinted by permission from
During curve construction for their subsequent use in solid models,
always be aware of impacts of creating and modifying geometry. Curves as
they are discussed here are a means of constructing complex surface geometry
that may not be developed directly by available functions.
Trimming Curves
Curves may be trimmed to other curves or boundary of curves. In the case
of lines and arcs, the results of trimming are well defined. In the case of
splines however, the resulting trimmed portion of the spline may differ
slightly from it's previous original state. Only those deviations within the
specified system tolerance are acceptable. Make a habit of checking spline
endpoints particularly if they should form closed connections with other
curves.
Extending Curves
Curves may be extended to boundaries or by specified distances. The
results of extending lines and arcs are predictable. Extending splines can
be unpredictable. Planar 2D spline curves can be expected to remain planar
after extension. Extending non-planar 3D spline curves are the least
predictable. If you extend spline curves be aware of local deviations and
make sure the resulting endpoints are where you anticipate them to be. If
you are unsure, constrain them by moving its endpoint.
Local Curve Modifications
Spline curves can be modified locally by adding, deleting, or moving
middle or ending control points. Always be aware of the results of such
modifications especially if other geometry is dependent of the affected
curve. Local curve modifications can be used to ensure that multiple curve
endpoints are coincident when they should be. See also Extending Curves
above.
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